Ultrasonic probes include a two-dimensional array probe having transducers arrayed in a two-dimensional lattice pattern. Since the number of transducers of a two-dimensional array probe is larger than that of a one-dimensional array probe, the two-dimensional probe needs to incorporate an integrated circuit (IC) associated with part of transmission/reception of ultrasonic waves. In this case, a flexible printed circuitboard (FPC) is sometimes placed on the rear surfaces of the transducers. The placed FPC is led from the rear surfaces of the transducers. The resultant FPC is connected to an IC-mounted board (referred to as an electronic circuit board hereinafter). In this case, it is necessary to output signals from the respective transducers. When outputting signals from all the transducers by using one FPC (for example, FIG. 11), the spacing between the traces of the FPC decreases. This may fail to obtain a proper ultrasonic image due to crosstalk between the traces. For this reason, some probes take a structure in which the overall two-dimensional array is divided into a plurality of modules (referred to as module division hereinafter) to provide FPCs for the respective modules, and the FPCs are sandwiched between the modules (for example, FIG. 12). There is also available a sparse technique of reducing the number of traces by reducing the number of transducers used for ultrasonic transmission/reception (for example, FIG. 13). On the other hand, some probes use, as an FPC structure, an FPC having insulators and wiring patterns stacked on each other (referred to as a multilayer FPC hereinafter).
When, however, performing module division, since the spacing between the transducers differs from the spacing between the modules, sidelobes occur, and a proper ultrasonic image may not be obtained. In addition, module division leads to an increase in cost due to increases in the number of parts and the number of manufacturing steps. The sparse technique may not obtain a proper ultrasonic image due to the adverse effects of sidelobes and the like on an acoustic field and a deterioration in sensitivity. A multilayer FPC leads to a high cost due to a complex manufacturing process. In addition, since the flexibility of a multilayer FPC is lower than that of a single-layer FPC, the multilayer FPC is difficult to handle in the ultrasonic probe. Furthermore, the multilayer FPC requires through-holes in the respective layers for electrical connection, and the through-holes cannot be used as wiring spaces. Therefore, the multilayer FPC is poor in efficiency in terms of wiring spaces.